1. Field of the Invention
The present invention relates generally to neck structures for plastic containers. More particularly, this is a neck structure having a flange with undulations on the top surface that exhibits advantageous top load properties.
2. Related Art
Plastic containers are now in common use for storing foodstuffs, medicine, liquids, and many other materials. These containers must withstand a variety of radial side wall forces and axial top loading forces during manufacture, shipping, storage and use. For example, containers filled using a hot fill process must be rigid enough to resist side wall collapse due to internal vacuums that develop as the hot liquid added to the container cools. As another example, containers are required to withstand radial forces during label application operations.
In addition to radial forces acting on the sides of a container, the container must also resist axial top load forces that act to compress a container. These forces arise at a variety of stages during the manufacture, fillings storage, shipping and display of containers for sales to consumers. For example, after initial manufacture, bottles may be stacked and stored. Although individual bottles are relatively lightweight, the weight of multiple stacks of filled bottles, as typically stored in a warehouse, is large, placing significant pressure or bottles at or near the bottom of the stack. Top load forces also arise during capping operations. During capping, the bottle must resist not only collapse, but also deflection of the neck as the cap is applied. If the neck deflects during the capping operation, the cap will not be properly applied, leaving an opening. This results not only in scrap bottle material, but also in wasted product.
Systems used to transport containers during the manufacturing process frequently lift the container at the neck using a fork-like apparatus. In order to be lifted or transported by the apparatus, the container is manufactured with a flange, also called a transfer bead, located in the neck portion of the container. Because of material flow properties the flange cannot be manufactured as a solid projection without an unacceptable increase in gram weight. Rather, such flanges are typically formed as a hollow outwardly projecting “V”, thus having an appearance similar to a single fold of an accordion or bellows. When topload pressures are applied to such a structure, for example during capping operations, the flange tends to fold, which results in a deflection that can lead to misapplication of the cap. This becomes even problematic during hot-fill processing. To overcome this problem, prior art solutions have included the use of larger amounts of material. However, increases in amounts of material, i.e. increases in “gram weight,” are undesirable; lightweighting of containers without a deterioration of physical properties can give a manufacturer a significant competitive advantage. Thus, increases in gram weight may result in unacceptable increases in cost.
Plastic containers, especially blow molded plastic containers, are manufactured in various shapes to achieve structural advantages and aesthetic function. Specifically, it is known to provide container side walls with troughs, extensions and decorative shapes to accommodate internal vacuum forces. Inward flexing of the side walls and panels may also be used to accommodate vacuum forces that develop during the hot-fill process. Inward flexing of the side walls accommodate volumetric shrinking but create undesirable corner deformations which reduce structural capability to withstand top loads.
There has also been some focus on the modification of the dome or bell portion of a container to improve top load resistance in that area. There has been less focus on strengthening of the neck portion of containers to improve top load resistance. However, as efforts continue to further reduce the weight of containers, the thinning of walls in the neck can become an important design concern.
There is a continuing need for bottle structures able to resist various forces that act on a container during manufacture, filling and use. The relative lack of focus on strengthening the neck region of plastic containers results in a particular need for designs that improve the load resistance of this area, particularly in regard to capping operations and other manufacturing segments requiring top load strengthening.